Hey guys, I did some searching and everybody else's issue seemed to be a constant hum, not sure what could be causing mine, but here's the situation (LS1/T56 FD):

At freeway speeds beginning at around 75 in 6th gear, around 2k rpm, if I'm cruising, I get a pulsating hum from the rear; it's loud enough that I can hear it above the radio. The hum noise is about 1 second per cycle, if you're counting 1-1thousand, 2-1thousand, etc. The cycle seems to get shorter the faster I go, but if I floor it, i can't tell if it goes away, or if the exhaust noise drowns it out.

Putting it in neutral or letting off the throttle makes the hum go away entirely. I tried cruising at 80 mph, 5th gear, around 3k rpm and it didn't seem like the hum was coming out, or if it was, the cycle was short enough where it sounded like my exhaust. I also tried cruising on local streets at around 2k rpm in various gears, and couldn't get the noise to come out.

What's weird is that this was happening with my old stock diff. I thought it may have been the diff, so I recently picked up a rebuilt t2 s4 LSD in a FD housing and put it in a couple weeks ago, but I'm still having the same problem. Im also not feeling any vibrations at all, just the noise. Any ideas?

 

It's probably just your wheels or your exhaust resonating.

 

hmm...I don't think it's the wheels since it only comes on when I input throttle.

Maybe it's an exhaust drone, but wouldn't that be a constant hum, rather than a pulsing hum?

 

wheel bearing. try driving on the freeway going at the speed when the noise come, change lanes (left and right) to see if the noise change. if the noise change when chaging lane then it your wheel bearing. ex. noise goes away when u change onto the right lane right wheel bearing. hope this help

 

I was thinking wheel bearing as well, can also do "the invisible slalom" to see if the noise changes. if you turn right, that loads the left bearing, ext.

Could also maybe be from the diff. Pinion bearing? side bearing? hard to say without hearing the noise, able to get a video/sound clip of it?

Jay

 

Rear universal joint of propeller shaft?

 

When I had a wheel bearing go out it was a constant hum. The pulsating means something is resonating. I have a buddy with a trans am and he put new tires on it and it gave me a headache from sitting in the back seat all I hear is waaaa waaaa wa wa wa wa wa wa wa.

Easy way to check the wheel bearing is jack up the rear and wiggle the wheel laterally if it wiggles then they are bad.

 

Took the car on the fwy today and failed completely at catching the noise from my iphone. It's definitely there but the phone speaker just can't pick it up.

Did this before my drive, everything seems tight.

How would I check for this?


During my drive, the noise was still there around 75-80 but it was quieter. I'm not sure what's going on, since I did the tranny fluid yesterday, took it for a drive to see what was up, and the hum was still very very loud. Left it overnight, basically just jacked up the car to test the wheel bearings, then today when I took it up to speed, it was a lot quieter.

 

To check the u-joint, unbolt it from the pinion and then drop it down. turn the 2 free caps, they should turn freely. DON'T pull them off unless you wanna go pin hunting, or have a clean work area the 2 point that are still on the drive shave, it should pivot between them smoothly. that make sense? :P