I have a 2001 Durrango R/T and I'll check evap solenoid tonight with someone in the car if we can match pulsating you describe with sound inside we might have her licked! I'll let you know what we found. If not exhuaust leek might be true aswell. I wish I just didnt care!!!!

 

I dont beleive it. Check your Transmision dip stick tube it may be rubbing on a bolt that goes through the firewall . If so just pull the whole dip stick housing forward away from the fire wall. Problem solved.

See ya and thanks for all the advice