I have 14 plate 500L 1.6 diesel trekking, last week or so the engine is making a loud vibrating noise, similar sound to an exhaust blowing, noise only heard inside, as I cant hear it when revving with door open, I am not convinced its the front exhaust, it seems to be coming from under the dash. it is very noticeable if revs aren't high enough for the gear its in, Ive booked it in for inspection next week, has anyone else had a similar problem?