Any further info on this? Did you find the problem?
Today after a five hour drive my fuel pump started to make the warbling noise during the prime only. (130+K miles on pump) Fuel pressure is good so the pump is working. I am just checking to see if there is anything else that may cause this or is it just the first signs of a dying fuel pump.
You know what? I never did find out. As a matter of fact, I ran it for about four hours on a cool day last September and not once did it make the warbly noise. Same as you, fuel pressure was fine and no performance issues.
I wanted to try and measure voltages on the pump (to rule out faulty wiring), but never made it that far. I was also wondering if it was some sort of venting issue since it only happened on hot days-but that is pure speculation...I am not a mechanic or even probably familiar enough with the system to make that statement; just my personal thought.
The only advice I can offer after spending a lot of money having a mechanic look at it (and it was only half done, since the issue was not fixed and they did not troubleshoot) and watching May03LT's videos and reading posts are:
1)The pump has 130K on it, it's probably time to replace it anyway.
2)Get an OEM pump.
3)Make sure the mechanic troubleshoots the issue and doesn't throw parts at it--check wiring, measure voltages, and anything else they can do with the tank off since you already paid the labor to have it removed.
4)Maybe replace the fuel filter, too? Especially I think the later years, the filter is a lot harder to access?
I am sure someone might offer something a little more useful, that's just my experience and I am not a mechanic. Good luck it was frustrating. I ended up trading it in for a Ford Expedition....I already miss my Trailblazer...it seemed more comfortable and I have already paid to rebuild the rear differential, a rear wheel bearing and front axle seal. Plus, it has a bunch of other minor "known" issues I need to fix someday....and my biggest fear....Spark plugs--it's a 2005 and I guess that 2nd gen 5.4 engine is known for plugs getting stuck in the block, yay!
If you do find a solution, I'd be curious to know what it is.