Michell Gyro Se running a little slow

I have noticed that some songs sound slower off my table than they should. This is most evident on Led Zeppelin's Whole Lotta Love, Simon & Garfunkel's Cecelia and The Smiths' Frankly, Mr Shankly. Most of the time, the difference is not noticeable, but on some songs I can pick it up. I'm not sure what the problem is. I have the external power supply but am not sure if that is the issue.