2000 Estima, 6 cylinder, makes a short whining noise on start up, also when placed into gear both forward and reverse - mainly when cold - makes a slight knocking sound that fades when you pick up speed, this knocking sound also goes away when the van warms up. any help very much appreciated, thanks.

Yes. You broke a circular tightening panel within the gear box, the part itself is cheap but getting to it is a lot of work so its quite costly. Nothing you can fix urself unfortunately.

Kindly state your MAKE and MODEL when asking for help with regards to your product or item.

you gear is bad you might have to overhaul it the band or cylinder could be bad it could be as much 500 dollars check your fuilds make sure they are clean and full ont over filled..

If the noise happens when car is in park and you rev it to about 1500rpm's then its thebearing in the oil pump of the torque converter.It should make noise all the time even in park ideling. You may need a rebuild transmission. Have the vehicle checked out at a transmission repair shop

4R100 or 4R70W?

Geartrain
Power is transmitted from the torque converter to the geartrain components through the input shaft and forward clutch cylinder.

• By holding or driving certain members of the gearset, four forward ratios and one reverse ratio are obtained and transmitted to the output shaft. The ratios are as follows:

GEAR RATIO 1ST 2.71 to 1 2ND 1.54 to 1 3RD 1.00 to 1 4TH 0.71 to 1 REVERSE 2.18 to 1
Input Shaft
The input shaft is supported by two bushings in the stator support. End positioning of the input shaft is controlled by the splines in the converter turbine and the overdrive planet assembly.
Output Shaft
The output shaft is supported by two bushings in the case and by the slip-yoke and bushing in the extension housing. End positioning is controlled by the parking pawl gear and snap ring or shoulder and by the reverse ring gear hub and snap ring.
Overdrive System
The overdrive planetary system consists of the overdrive planet assembly, overdrive sun gear, overdrive ring gear, coast clutch cylinder, overdrive one-way clutch assembly and the center shaft, as shown in the following illustration. The overdrive planet assembly is splined to the input shaft. The overdrive sun gear is centered by a bushing on the input shaft and held in place laterally by needle bearings on the reactor support and the overdrive planet assembly. The overdrive sun gear is splined to the coast clutch cylinder, which in turn is splined to the overdrive one-way clutch inner race.
The outer race of the one-way clutch is splined to the overdrive ring gear, which is splined to the center shaft. The center shaft is centered by the forward planetary assembly and is laterally held by needle bearings on the center support and the overdrive planet assembly. The center shaft is splined into the forward clutch cylinder.
Two friction clutches are assembled in the overdrive planet assembly. The coast clutch is splined between the coast clutch cylinder and the overdrive ring gear. The coast clutch is activated to perform engine braking in MANUAL 1, MANUAL 2 and third gear with the transmission control switch engaged.
The overdrive clutch is splined between the case and the coast clutch cylinder. The overdrive clutch holds the coast clutch cylinder and, in turn, the overdrive sun gear, to permit the planet assembly to overdrive the ring gear.
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Forward Drive System
The forward drive system consists of the forward clutch cylinder, intermediate brake drum, intermediate one-way clutch, input shell, forward ring gear, forward ring gear hub, forward/reverse sun gear and the forward planetary carrier and forward planetary gears.
The forward clutch cylinder is splined on the center shaft. The forward ring gear is piloted on the forward ring gear hub. Thrust bearings on the forward planet assembly and forward clutch cylinder hold the forward ring gear hub in place.
The intermediate brake drum is radially supported by bushings on the center support and is laterally controlled by thrust washers on the forward clutch cylinder and center support. The intermediate brake drum has the inner race of the intermediate one-way clutch press-fitted on its pilot. The intermediate one-way clutch's outer race is splined to the intermediate friction clutch, which is splined to the case. The intermediate brake drum has lugs that are slotted into the input shell to form a mechanical connection. The input shell is splined into the forward/reverse sun gear. The forward/reverse sun gear is common to two planetary gearsets. The forward planet is splined to the output shaft and is laterally positioned by needle bearings on the sun gear and on the forward clutch cylinder, as shown in the following illustration.
Two friction clutch assemblies, the direct clutch and the forward clutch, are shown with the forward planetary assembly. The direct clutch assembly splines the forward clutch cylinder to the intermediate brake drum. The forward clutch assembly splines the forward clutch cylinder to the forward ring gear. The forward clutch is activated during all forward gears. While in third or fourth gear, both the direct and forward clutches are applied to hold the forward planetary assembly and enable it to act as a solid shaft.
In second gear, the intermediate clutch assembly holds the forward/reverse sun gears. It is applied, along with the intermediate one-way clutch, to hold the intermediate brake drum, input shell and forward/reverse sun gear. In higher gears, the one-way clutch overruns.
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Low and Reverse Drive System
The reverse planetary assembly consists of the reverse planetary carrier, reverse planet gears, the reverse ring gear, the reverse ring gear hub, the reverse clutch hub and the low-reverse one-way clutch assembly.
The reverse ring gear hub is splined to the output shaft and to the reverse ring gear. The reverse ring gear hub is laterally held by a needle bearing on the inner race of the low-reverse one-way clutch and a snap ring on the output shaft. The reverse planet assembly is splined to the low-reverse clutch hub. The low-reverse clutch hub is connected by the reverse clutch to the case. The inner race of the one-way clutch is bolted to the case.
The reverse clutch assembly is activated in REVERSE gear and in MANUAL 1. The reverse clutch bypasses the reverse one-way clutch during coast and MANUAL 1. The reverse clutch holds the reverse planet assembly in REVERSE gear to enable the sun gear to drive the reverse ring gear in the opposite direction.
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Apply Components
The following information describes the operation of the three 4R100 one-way clutches.
One-Way Clutch—Overdrive
The overdrive one-way clutch, shown in the following illustration, transmits engine torque from the overdrive sun gear to the overdrive ring gear in first, second and third gear range. The overdrive one-way clutch transmits power when the sprags are engaged between the inner and outer races. The inner race is splined to the coast clutch cylinder, which in turn is splined to the overdrive sun gear. The outer race is splined to the overdrive ring gear.
The overdrive one-way clutch engages whenever the overdrive planetary system attempts to drive the overdrive sun gear clockwise when the overdrive ring gear has a counterclockwise torque from the vehicle. When torqued counterclockwise, the overdrive one-way clutch engages and acts as a wedge to lock the sun gear and the ring gear together. During coast, the overdrive one-way clutch enables the ring gear to overrun or spin at a faster rate than the sun gear.
The overdrive one-way clutch overruns when in overdrive (fourth gear). In overdrive, the coast clutch cylinder is held by the overdrive one-way clutch, which in turn holds the overdrive sun gear. This causes the overdrive planet assembly to walk around the sun gear and overdrive the overdrive ring gear. The inner race of the overdrive one-way clutch is thus held stationary while the outer race is allowed to overrun clockwise.
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it does sound like the transmission has packed it in. you might be able to find a decent used one via a wrecking yard and get a local mechanic to install it.
try to find one out of a car with under 100K miles on it.

First thing I would check is Automatic transmission fluid level, you can't fill the clutch packs if there's no fluid available in the pan to do so. Does it move in forward or reverse, are there any whining/grinding noises from underneath?

the whining noise is the torque converter and trans oil pump,this needs replacement,reverse is probably clutch pack or a gear set

Just a thought- remove the oil filler cap when the whine is present - (this checks if PCV valve is faulty, causing high crankcase vacuum, which in turn causes a whistling/whine noise as air leaks past engine oil seals). Worth a check.

Try listening with a short piece of hose pipe to locate immediate area/source of noise.

If it's only happening when you initially place it in those gears before going forward or reverse, your U-Joint in the rear is going bad. Replace both when you replace the one. This way you don't have to go there again when the fron U-Joint decides to go out. Cheap insurance.

hi my name is nathan .......now...... what it sounds like is #1 (I have to hold it in place til I get to second gear) that can be that your shift linkage is worn or out of adjustment,pilot bushing is Badly worn,shift fork,lever and or shaft is bent or worn,or your bell housing is misaligned or just loose...i have a few more ideas on why it is jumping out but those are the main ones now about your whining gear noise#2( The whining sound starts low pitched in each gear then gets higher pitched as the rev's increase) you may have worn gears maybe or it could be just that your transmission lubricant is incorrect or inadequate.