Today while stuck in parking lot traffic in my stock 91 vert, I got this banging noise. It happen like 3 times consecutively, and 3 more times a couple minutes later (while inching forward in line) after the second time it stopped. Nothing changed, the car still runs fine, but I honestly want to know what could possibly cause that noise.

It is comparable to something hitting the bottom of the car. I once had a power steering belt shread and slap my hood many times before I figured out what it was. It sounded exactly like that, but my belts are fine.

The ac was on and afterwards it made this weird noise like there was air going into the condenser, but it continued to work fine and the air sound went away.

Very puzzled.

 

Auto or 5 speed?

 

5 speed

 

And when I'm creeping fowards in traffic I don't really let the RPMS go past 1500

 

Were you going fast enough for something to stick to the tire, bump a few times in the wheelwell, and then fling off? Could be as simple as that.

 

No, I was in a parking lot with people in front of me, so I was just creeping. But it sounded like that

 

Loose or broken front diff mount.

 

This would cause such a random occurance?

 

Yes, that or your trans mounts are gone

 

Okay. It's only happened once, but I will lift the car and look into it, thanks guys. Much appreciated.

 

at a stop light, dump the clutch. banging noise?

that will tell you instantly if its a mount or not.

 

I have tried to recreate the sound by doing that and under hard acceleration. No luck.

 

You sure your clutch just wasn't clattering?

 

Positive. That's a completely different sound.

 

Just checking.

 

well if its not happening and you arent able to recreate it, i guess leave it alone till it happens again.

 

Today I will lift up the car and check all the suspension components/bushings, Brake components, as well as motor, transmission, and differential mounts.

 

Today I found a ballpark idea of where the noise is coming from. It happened at the same place around the same time today, only this time the car was idling. It seems to be coming from the AC system. I got in the car let the engine warm up and the ac cool down for about 3-5 minutes. I moved the car maybe 10 feet and stopped and then the loud banging commenced. Like someone hitting the fender with a hammer. Only this time. I noticed that after it happened the condenser or refrigerant lines in the dash started making all sorts of hissing get noises. I turned off the AC and the banging and hissing went away. Any reason why the AC would make this noise? It has been converted to R134A.

 

bad compressor? bad condenser? does it sound like the bang is coming from inside the dash?

 

I can't really tell for sure. It sounded more like engine compartment to me though. Is there any reason for any of the AC components to make a banging noise?

 

A sticking restrictor /hblock will cause a knocking and hissing sound. Causing too much of a restriction.

 

Sounds like a good place to start Craze8. Where might this restrictor be located?

 

If its what i think he is referring to, get ready to pull your dash

 

Its on the evaporator under the dash

 

Which everyone makes such a big deal over but is actually quite simple.
The first time might take 1-2 hours as you puzzle out the sequence but thereafter, it's a 20-30 minute job.

Two hints:
Remove the steering wheel

Undo the ebrake from the tunnel and let it hang

After everything is undone, I sit in the drivers seat and lift the dash over the steering column and remove through the passenger side.
It's awkward but completely possible working alone.