Blow buy/slight knock

Hello,

Have a 99 Beetle with 129,000. Starts, runs and drives great. No smoke ever. I am getting blow buy out of the oil cap...is this normal??

I also am getting a slight knock at idle, after driving for a while. Sounds like it is just behind the firewall on the middle to right side of the engine. Open the door and u really cannot here it but close the door and you can here a slight deep pitched kinda knock. Do I have an oiling problem...PCV valve clogged??? Not real familiar with these cars so any suggestions on what to look at would be greatly appreciated.

Thanks, Erich