Electrical hum in cab of '96 Chevy - radio off

[ECeptor]

About a month ago I noticed an electrical humm in my cab that goes up and down in frequency with the engine rpm. It sounds exactly like a poorly installed radio will. However, it's the stock radio and it never existed in the previous 145,000 miles.
It's a 1996 K1500 4x4 w/ the 5.7L engine. I assume it is some sort of grounding problem, but have no idea where to start. The plug wires are the originals. Last year while hunting for a hard starting issues I took all the ground wires from the battery to the block off, removed any corrosion and put them back on with dielectric grease.
Any ideas on what to check?

[Sweeney]

I'd start with new plug wires. Originals are good for about 50,000 miles before the insulation begins to break down.

[Just Tool'n]

Did you change spark plugs lately?
If so did you get the resistor type if so, a long time ago, that is what use to cause the noise!

[Daytona100]

Sounds like an alternator whine. Take the belt off and see if it goes away.Pretty common on GM vehicles. :idea:

[ECeptor]

Sounds like an alternator whine. Take the belt off and see if it goes away.Pretty common on GM vehicles. :idea:
I'll try that. I did notice last night that the voltage gauge was moving around more than usual. I checked at the battery at idle and it had 13.8V.
As for the plugs, they were replaced about 2 yrs ago and the problem just showed up.
As for the wires, it might be that, but I'm going to look into the alternator first.
Any other ideas or things to check?

[monkey rage frank]

I had a friend with that year truck. sounds like the same problem. Make sure you check the radio. He had a stock radio and a wire must have came loose, truck burnt to the ground. Good Luck.

[ECeptor]

I had a friend with that year truck. sounds like the same problem. Make sure you check the radio. He had a stock radio and a wire must have came loose, truck burnt to the ground. Good Luck.
Holy crap! I'll tear into the dash this weekend and double check everything.
When and how did it burn? The reason I ask is I park in my garage and really don't want to burn my house down and kill my family in the process!!!

[monkey rage frank]

He was driving back from Mammoth and saw some smoke and puuf there it went. May have been an only case, but I'd hate to hear about it and thought later I should have told him. Good Luck

[ECeptor]

I just replaced the alternator. It isn't humming anymore, but time will tell since it was an intermitten problem.
The battery only had 12.08V at lunch today so a dying alternator sounded like the most likely cause.
Thanks for the advice everyone. I'll post again if the problem isn't solved.