Quick question regarding the fuel pump: Does it stay on at higher pressures when at speed? Or is it purely RPM dependent?

The reason I ask is, recently I fixed an exhaust leak which quieted up the car a bunch. I noticed a humming coming from the rear, which sounds extremely like a fuel pump. I was worried it was the differential, but it wasn't really a gear noise, more of a fuel pump buzzing. So, since this noise starts up around 40ish, I threw it into neutral (clutch out and all) while at that speed wondering if that noise would drop with engine RPM. It didnt. Should I start to look for a new diff? Or is it very possible its the fuel pump? Its not extremely loud, its just sort of...there. Doesn't sound like road noise but I do have some noisy tires. The last few times I changed the diff fluid (last one, roughly less than 5K miles ago) there was the normal black sludge on the magnetic bolt but no chunks. Running Valvoline full synth currently, recently changed from the M1...

-edit-

I haven't been rough with the car lately (growing up, sadly) but when I did purchase the car maybe 3 years ago I did do a decent amount of launches, both at SCCA and on-ramps. Never found chunks of anything in the diff (I do a lot of diff fluid/trans fluid changes...just cuz.)

 

Fuel pump power is not PWM modulated to adjust for duty cycle. It's always spinning at the same rate and not dependent on RPM or speed.

The pump may change in tone as a function of voltage. This can be noticeable at idle or when the AC compressor is kicking in. But other than this small voltage shift, the pump is always flowing the same rate.

 

^gotcha, thanks. So its definitely something speed related then. I wonder if its just the tires...