Neon 95 has nosises around or inside the timing belt cover! PLZ HELP!

My car Info: - Dodge Neon 95 - Has about 140,000miles - Poor maintenance except some oil changes. - SOHC Engine 2.0L
The neon used to overheat and had a head gasket problems before, I
fixed it the cheap way by putting the Blue Devil and all was good since, no overheating, no leaks... that thing is great!
A little more than a month later, a noticeably loud knocking noise appears to be coming from or around the timing belt cover. I don't know if the timing belt is hitting the cover from the inside or something hitting the cover from the outside. To me it sounds like something hard is hitting plastic, but I could be wrong.
The mysterious part is that the noise disappears completely when revving the engine, or keeping it around 3000RPM and above, below those RPMs the knocking noise comes back again.
I have also noticed some stalling when accelerating on the road, especially when getting up to speed for the highway... but no problem starting the engine in the morning, except the noises of course, which is getting louder every day.
I am thinking it could be the timing belt/water pump, but I am not sure... any insights will be appreciated?
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