2000 TL whistling noise until loosen the oil filler cap

[dhspring]

anyone seen an engine whistling noise at idle speed iin a 2000 V6? I accidentally found what is causing it --when I loosen the oil filler cap and allow air to get in to the valve cover the noise stops. It's pulling a slight vacuum and loosening the oil filler cap allows air in and the whistling noise quits. There is one a PCV valve on the back valve cover nearest the firewall that seems to be okay, but something else must be plugged up and that is preventing air flow into and around the crankcase and thus the whistling occurs. There's a diagram on the hood that shows 2 "FIVC" valves connected to another module, but I cannot locate them on the engine at least on the top, they may be underneath. Strange situation, but the noise is eliminated by leaving the oil filler cap 1/4 turn loose from tight. Not what I want to do to fix it, so any suggestions are greatly appreciated! Thanks in advance.