I ordered 2 set of JBL 2ohms about 3 years ago and recently the front speakers cut in and out. Thinking that it was the JBL speakers that is acting up, so I put all the OEM speakers back into the car and the front speakers works again. An hour later, the front speakers stop working again. I also noticed the JBL speakers are 4ohms. I ran those JBL for over 2 years without an aftermarket amp and listen at volume level 20+. What could be the problem? Is the head unit and amp messed up?

Also there were grease founded in the front speaker connectors. Is this normal?