Whining/grinding noise at deceleration

the fact that on attaining speed the problem resolves itself indicates that it is not a diff problem
problem diffs will be noisy under acceleration, deceleration and at sustained speeds
it indicates something under load like failed cv joints, drive shaft "U" joints or wheel bearings
If you have not replaced the cv joints in that mileage , then that is the area I would be concentrating on first

Depending on which side, it could be a wheel hub assembly or drive axel/CV joint/UJoint worn. If from the center of the vehicle it may be an internal differential problem

This can be caused by several different things, such as: A bad axle shaft, the differential or transaxle bearings. The ring and pinion drive, wheel bearings etc. Any one of these will cause shaking and noise on deceleration. Check transaxle fluid level, raise vehicle front end and check for slop in the wheel bearings and check for noise while spinning the tire. The wheel bearings will often make noise when lugging down as you put it due to the weight shift to the front wheels. This also applies to the axle shafts and CV joints and the differential.

Probably a bad CV joint on one of your drive axles to the front wheels. You have two drive axles coming out of the transaxle, one to each front wheel, and both have an inner CV joint where they enter the transaxle, and an outer CV joint where the axles fit into the wheel hub. (A CV joint is really like the old U-joints, serving the same purpose.) A clicking noise on turning is usually a badly worn outer CV joint. The cheapest fix is to buy a remanufactured half-shaft for your car. That is the axle shaft with both CV joints at each end inspected and reconditioned with new grease and CV boots installed. You need to know which side is bad before buying. The half-shaft is sold ready to install. Someone with good mechanical skills will need to remove the old one and replace it with the new reconditioned axle shaft, or half shaft as they are also called. The last time I bought one (about two years ago) the cost was reasonable- about $65.00. That is less than the cost of one new CV joint.
Hope this helps you out.

Drive axle in front

Auto or 5-speed?
Subarus have CV axles in front and back. And a drive shaft from the center differential of the transmission to the back differential.

Yes, it could be the drive shaft or axle. If you turn the car hard left or right do you hear any noises - usually a 'clicking' sound? This is likely a CV axle in front.

Check the fluid in the transmission (Automatic) (info is in the Owner's Manual) to make sure it's full and/or gear oil in the front differential.

If it's an Automatic transmission, the fluid may need changed - NOT FLUSHED - if it has more than 30K miles since last changed.
GL,
TD

A clicking noise heard especially while making a turn is most likely a CV (constant Velocity) drive axle(s) that is worn out, and if the CV boots are torn and dirt has been getting into the drive axle CV joint, then replace the CV drive axle assembly and do not have the drive axle re-built or re-booted, especially when you can purchase a complete new CV axle assembly for under $60.00 and here is a link to check one out.

http://www.familycar.com/store/item/Chevrolet_Malibu_Replacement_Axle-Assembly_1997_2003_ARBC507101.html

If it is wheel bearings the noise would be there all the time with a growing whine as you accelerate, to me I would say the drive shafts {CV joints} need to be replaced. Sorry to bare the bad news, Remember we are here to help as best we can, good luck

CV Joint Axle Replacement - How to Repair or Replace

Over time the rubber boots of the CV joints can become cracked, torn, or otherwise compromised. Once moisture and dirt get into a CV joint and grease makes its way out, the CV joints days are numbered. Signs of impending failures are a click-click-clicking or metallic crackling noise while turning and accelerating or a clunking upon deceleration. While one can repack, reboot, and rebuild CV axles, it makes more sense for the average do-it-yourselfer to procure replacement units and swap out the old axles. If a boot is torn or missing, it is possible to save the joint if caught early enough, but usually the damage has already been done. Replacing or servicing the entire CV joint axle assembly may be the smarter move since replacing a boot may involve removing an axle, which may also involve removing half or all of the vehicle's brakes and suspension.

on this type of vehichle, you have two axles in the front; one going to each side. Chances are that the boot at the axle joint was torn and that is why you are having problem. In teh past people used to replace the boot, this day and age its actually cheaper to replace the axle. So you would need to replace that side of the axle (the half shaft).