no.this is normal.I've been running synthetic oil for awhile,and just recently switched back to conventional oil because of not only this,but also a rattling noise at 2000-2500rpm under load.synthetic oil ALWAYS is thinner than conventional oil(when comparwed with the same weight).the next oil change,maybe try a thicker weight oil (just one weight up,like if you're running 5/30 now, try 10/30 or 10/40).