TRlGGER

Well since ive bought the car, in idle the oil pressure will drop from 40 to 30 and when that happens the car starts to shake a little, sometimes it feels like it may turn off. So i took it to a GM specific racing shop to see if they can give me any pointers. They said to switch from Mobil1 5w30 to Valvoline VR1 10w30 cause my car is a 99 at 70,000 miles. Today i switched it to the VR1 and now in idle the engine knocks on the passenger side. When i put in park it doesnt. Only when its in drive or Reverse (A4)

Thanks for any opinions or suggestions!