i have been getting this strange humming only when i am on the gas, when i let off it goes away completly...

any ideas as to what could be causing this? is it normal?

its a 98 4x4 blazer

 

It is very possible that the cruise control cable is resting against the PCV hose and you are hearing the operation of the PCV valve. The PCV valve is located on the drivers side valve cover and it has a hose that goes straight up off of the PCV valve, 90* bend for about 3-4" and another 90* bend down into the intake manifold.

I recently had this issue as well. I ended up bending the bracket that the cruise and throttle cables attach to in order to create a gap between the PCV hose and cruise cable.

Good luck!

 

Like Kyle said "It is very possible that the cruise control cable is resting against the PCV hose..."

I think I read a bulletin on that sometime ago. I hope that's the case with yours, it's a lot cheaper than some of the other possibilities.
Let us know what you find.

 

Yep!! I'm 99% sure thats where my hum is coming from, I can even feel it on the gas pedal. I've just never got around to separating them mostly because theres a clip right where i need to bend it.

 

hm i got to talk a quick look at this today, and i cant quite follow what you mean. i see where the cruise and throttle cables run but im not sure i can pin point the spot where they would be resting on anything they shouldnt be...

i should be able to take a better look tommarow and also i will look through my service manual to get a better diagram of what im looking at...

 

i have determined that this isnt the problem...i am thinking a u-joint?

 

I would be concerned that you have worn diff bearings.
I'd put the truck on jackstands and see if I could hear or feel a vibration at the rear diff

 

I had the same problem for over a year and with my busy schedule i never seem to have enough time to take it in or worse be without my vehicle for days. As a result it was the diff bearings, and they completly failed and I had to rebuild the whole rear end. Due to the limited slip, possi and because it has the larger 8" rear it cost me $ 1550.53. You should have seen the damage it was impresive looked like i milled down thearea where the bearings ride on a lathe. In the future if i ever hear any noise at least i will brring it in immediately. Now it runs great just the driver side door hinge is missing the bushing or something like that seems like a common problem.