Why does my 2005 bmw 325i series have a burn smell coming thru the a/c vents.

I just had an oil change and fuel pump replaced and after that is when I began noticing the smell of burnt oil/rubber. The smell is faint, but when I am at a drive thru with the window down it is really strong. I was told the A/C Compressor could be going out or the Valve Cover Gasket needed some work??