Engine stalling symptoms

[Beachie]

Hi

I have an A6 C6 Avant 2.0 tdi manual. I have a problem at around just under 2000 rpm, where the car seems to kangaroo but very quickly, almost like the brakes are being applied at about five times a second. It's more noticeable in lower gears and does not happen all the time but does seem to be getting worse. When it does this there seems to be a 'chirping' sound coming from possible the engine or the front of the car. It feels as if it's engine related as when you push through it, normality resumes. Anyone come across this or have any ideas? I have had the car about six weeks but I noticed it about four weeks ago.