bighead

The other day I noticed a new noise coming from the rear of my car, it's a humming noise (similar to tire noise) but:

• is only noticeable above 25mph
• isn't super loud, but constant
• isn't RPM dependent
• pitch/volume increases with speed
• doesn't change if I'm off throttle, on throttle, in gear, in neutral, clutch in, clutch out, or turning
• no vibration
• no rattling
• no clunking

The car drives smooth just like it has always done, I have 225/50-16 Bstone RE960AS (new this fall) and they have been practically silent until now. I haven't been able to inspect anything under the car but I wanted to get some opinions so I can figure out what to look for when I do.

Last year I replaced both rear wheel bearings (and it doesn't sound like any wheel bearing noise I've heard, either)

Autox/HPDE season is starting soon and I don't want to break anything my first event out...

TIA

Sideways

Fuel pump? It is mounted just behind the driver.

bighead

perhaps.. I'll check that on my way home from work.

Spec_Ops2087

fuel pump or could be normal gear whine

bighead

just an update, I don't think it's the fuel pump since it doesn't change with RPM changes and I can't hear it while idling (I removed my rear tray prior to this and it's not coming from that area)... I couldn't hear it while top down but I do think it's gotten louder (I drove top up to work this morning.)

Just thinking about it, it can either be my drivetrain past the tranny (prop shaft, diff, axles, bearings) or my tires (they are wearing evenly and are properly inflated)...

S2KPUDDYDAD

Drain the diff and check for damage. If you find metal in the oil or large metal parts on the drain plug....you found your issue

HankookS2K

sounds like a diff issue to me as well

my diff started to whine and i thought it was the tires, or something else. turned out my diff was days away from failing

bighead

thanks guys, I figured it was the diff... crazy that I was just doing some offseason highway driving too... I have some LE1605 coming from HTG for a mod day next Saturday but I think I'll pick up some mobil1 at advanced so I can drain and check the drain bolt for shavings...

bighead

one question, does anyone think it could be a CV cup issue? Can the CV cups make this kind of noise without vibrations?

bighead

just an update, I drained the diff and there was only the normal amount of metal on the drain bolt.... I replaced the LE607 for some Mobil1 temporarily until I get my 1605 in. The noise is still there and described by my friend as more of a whirring then a humming. He also concurred that the noise is coming from the left side of the car... Stupid me didn't check out the CV boots while I was under there... Should I swap cups tonight just to be on the safe side?