hi I have a audi a4 2009 b7. for the last few months there has been a rhythmic thudding noise from air box on idle (driving me nuts!) the power is also slight decreased. it has been in local garage but they couldn't find an issue. I have changed EGR valve, MAF sensor, did a DPF region, oil+filter, air filter and engine carbon clean but still hasn't fixed the issue. it has 70,000 miles the car. if anyones got any ideas on what to try next please let me know! Cheers 

Have something similar going on with mine. MAF sensor died so cold start and idle makes engine “pulse” and there is the thud from the air intake. 
I got a new MAF sensor and it didn't fix it. However, when i unplug the sensor, the car idles perfectly and the thudding goes away.

Don’t know what to do as clearly the car should have a working MAF sensor but seems to only run properly when the MAF is unplugged?????

It is the camshaft has worn through the buckets, had the same on mine about a year ago.