Clatter at higher revs, 1.9 tdi

Hello

I recently changed the coolant in my octavia 1.9 tdi. I took it for a good hard drive to get any air locks sorted out, but shortly into the drive I heard a clattering sound which happens when I hit about 3000 revs upwards. It sounds like a pile of stones in a wind tunnel. Its quite loud, and wasnt there at the start of my journey. This happens when the car is stationary also. I cant find anything loose, although I have yet to jack it up and look underneath. It appears to be coming from in front of me as the driver. I originally thought it was dirt stuck in the front drivers side wheel. What could this be? The car had a timing belt change 1000 miles ago, and I noticed the guy had the car stripped to bits. Im hoping its loose bolts(!) I do remember a bit of a vibration boom around the same revs for a while before this happened. The car seems to be driving fine otherwise. Could this be the turbo? Would it not effect the performance?