I have a humming noise on my 2006 rendevous when you start to slow down and then you hear it all the time when you start to accelerate and also a clunking noise when you put it in gear.

I would suspect a loose baffle in the exhaust system. Once I put an overhead rack on my F250 and when going down the road at a certain speed the air rushing between the overhead bar and the truck cab caused low hum.
When the noise starts ,and it is safe, put the transmission in N and see if it goes away. I have also shut my engine off while driving to see if a noise goes away. Usually it is a vibration problem.

Check fluid in rearend.

If the noise appears to come from under the hood/engine area, suspect a bearing in one of the accessory pulleys to be causing the noise. ( Alternator/AC compressor/idler/tensioner etc ).

Sounds (pun intended) like a problem with the differential (that globe that connects to the drive-shaft and to the two rear tires. Maybe, one wheel has bad bearings, adding resistance into the differential.

Is it a squeel or a hum / rumble? 1st run your hands around the tyres especially the inside. Check for hi and low spots on the tyres. If the tyre is hi low hi low hi low it makes a shocking sound. if it is a squeel noise have they checked your brakes cause brakes have squeelers to let you know they need changeing

Could be a Wheel Hub Brg Assy, on front

If you remove the caliper & rotor .You may
feel the bad bearing by hand

No other test than what your hearing around 35 to
40mph.

That loud humming noise you are hearing is the wheel bearing. After hitting the curb the bearing took a hit and became a little wobbly and over time the grease has seeped out and started causing the humming.So just replace the wheel bearing and anything else that might be loose or damaged like the tie rod and ball joints. if those issues are not corrected it might happen again down the road. good luck and glad to shed some light on your issue

Check your disc brake pads to see if they are down to the wear indicaters. When brakes are worn it creates a metal on metal grinding sound when vehicle picks up speed but will intermittenly stop when pressure is applied to brakes. Note that front brakes will be replaced 2 to 3 times more often than back brakes due to the front brakes being your primary souce of stopping power.

Most certainly,as well as, power steering,coolant,brake fluid,and check both diff levels.