Engine / exhaust noise care to take a stab at what it might be?

[SirRobyn0]

Truck 1984 Chevrolet C20 305. It's always had somewhat of a minor putting noise, but recently it has become more obvious. I generally cannot feel it, or barely feel it in drive, but in park there is some pretty obvious rhythm. Going down the road the truck runs great with no odd noises or sensations. I checked the vacuum at idle, the gauge needle read 20 and stayed nice and steady. I checked the base ignition timing and made no adjustment. It never does this when the engine is cold, even after it's come off fast idle. Gotta drive it 20 minutes or so before this shows up.

I'm thinking it's a weak exhaust valve or spring. What do you think?

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[squaredeal91]

I've heard other engines sound like this. Probably something w/ valves. Odd question. But Will it try to suck up a dollar bill at the tailpipe?

 

[SirRobyn0]

I've heard other engines sound like this. Probably something w/ valves. Odd question. But Will it try to suck up a dollar bill at the tailpipe?

Not an odd question to me, I test I've run and shown others that trick. I have not tried it on the truck but should.

 

[fast 99]

Valve guide wear? Baffle in muffler? Have seen that a few times. Doesn't always show on vacuum gauge.

 

[SirRobyn0]

Valve guide wear? Baffle in muffler? Have seen that a few times. Doesn't always show on vacuum gauge.

I'm right there with you on the vacuum gauge thing. I don't think the sensation that is there would be present if it was baffle in the muffler.

Basically you and @squaredeal91 backed up my thinking, but you never know sometimes someone will see or hear something different. I will do the tailpipe test with a shop rag the next time it does this. The entire drive into work today and it did not act up, so we will see and I will report back.

Thanks.