What's normal for inline HP fuel pump noise?

[joeydurango]

Just finished up a ~2200 mile road trip in my recently "completed" '72 K10. Running a 5.3 LM7 and a 4L60, pretty standard swap. We ran stock tank, gravity feed to basic inline filter, then to a Walbro high-pressure fuel pump, and a second, nicer inline filter. For the first several hundred miles on the new setup - before leaving on this last big trip - the pump's noise was consistent, a quiet whine you could hear when you were stopped but nothing loud or obnoxious. We left on our trip and after about 400 miles, the pump's whine increased in both pitch and volume, until you could hear it while driving at 40mph. I assumed it was having trouble getting fuel and changed out the first inline filter - it was packed with large detritus from the tank (thanks, guy who brazed in the fitting!). This quieted the pump back down to normal volume and pitch, and it was great for the next ~1000 miles. Then back came the noise - and I swapped out the filter again, only to have no effect on the pump. We ended up driving another 400 miles back home to finish the trip, with the pump making what seemed to me quite a lot of noise. Drove fine, no starvation or anything, just noisy. So:

The noise is annoying but I can deal. Just want to make sure I'm not burning up the pump. Has anyone else noticed a lot of variation in the sound of Walbro pumps? Or is this an automatic "something's not right, check it out"?

The one other thing that appears to have an effect is ambient air temp. Every time it's been excessively noisy, it's been 90 or above. I changed the first filter just as it cooled off for the night, and then drove around on the coast for the next week. Here at home it's not often super-hot. On the last leg of the drive back, it was hot before AND after I changed the filter, and no difference was apparent in the pump noise. Does this make any sense at all, or is it coincidence? Thanks guys!