A progressive humming noise as I drive.

[Yogi'sQ45]

I have a 94 Q45, and as I am driving there is a humming noise that seems to be coming from the back of the car. I replaced the rear tires, they needed replacing anyway, but no change. Any ideas? Thanks, Mike

[maxnix]

Nest of bees in the trunk?

Think about your fuel pump. Read Tangalora's excellent post.

Don't drive until it's diagnosed correctly.

[Q45tech]

Progressive like with speed increases...............differential, wheel bearings?Vehicle mileage and maintenace intervals of replacing diff fluid?

Usually diff and wheel bearings last ~~200k.

[goody90q45]

Nest of bees in the trunk? Think about your fuel pump. Read Tangalora's excellent post.

The fuel pump is in the gas tank which is behind your rear seat. Open your trunk and listen. At idle, if you hear what sounds like a swarm of bees coming from inside the gas tank it's your fuel pump. You'll need a new fuel pump and probably a Fuel Pump Control Unit (FPCU). Both are easy to replace and the DIY steps are in Tangalora's post which you will find archived. Good Luck.

[Yogi'sQ45]

Thanks for the responses! Yes, the humming noise or pitch increases as the speed increases and vise versa. I don't hear until I reach ~15mph. It has 142,000 and I've had it for 2 1/2 years and have not done anything to the differ... or wheel bearings. Thanks again for the quick response. Mike

[maxnix]

No fluid change?

[Q45tech]

The next step is to place it on a safe 4 post /point lift and drive the wheels to speed whicle listening under the rear with your automotive stethoscope to identify the exact NOISE SOURCES.

Make sure diff is refilled with new lube first.

Failure to drain and fill diff every 2 years or 30k is a sure way to spend $3,000 faster than you should by replacing diff.................eveny iffy high mileage junk yard units are $300-$400 plus installation and who knows if they will be better or fail soon.

[qsiguy]

While not in the rear of the car, the transmission mount can cause annoying hum. The sound would change with speed/rpm and when I replaced it along with the related exhaust mounts the hum was gone.

[bullittandy]

It could be the timer of a bomb planted by one of your enemies.