I have 1991 YJ Wrangler, 2.5 4 cyl with an engine noise. When the engine starts cold everything is great. Within 4 to 5 minutes I hear what sounds like a lifter noise in the front of the engine. I thought it might be the timing chain so I installed a new timing chain kit, replaced the chain, gears, etc. There's no marks on the cam, etc. After installing the timing kit same problem. When I get up to above 1500 RPMs the noise returns. Any ideas?