Digital distortion on playback of some audio trx

If load a project with just audio tracks (same type and bit rate and KHz etc), some will playback fine and others glitch and produce loud bursts of digital distortion. This is the same if I record audio into a project. Another weird effect is if I have two audio tracks in the project window, one will play fine, and the other always is messed up, even when they are put on the same track running consecutively. The distorted one will even play very short bursts of the muted good track in between digital noise and clicking. All audio files play perfectly in media bay. Recording audio is also perfectly fine.
I am running C7 on Win7 64bit with an Emu 4040 all with the latest drivers. Please help if you can