Strange sync problem which sounds like tape machine wow

[norfolkmastering]

I was recording some piano today using Sonar and a single USB connected MOTU interface set to internal sync source.

On playback I heard what could only be described as momentary speed variations, just like tape machine wow.

I loaded up a test tone into Sonar and played it.  Sure enough, I'm getting occasional random 'wow' so little speed variations almost as if the master clock in the MOTU is varying.

Sonar clock is set to Source Audio as I always use.

This is the first time I've ever come across this and I'm at a loss as to what to do.

[Xoo]

Ultralite?

I've had this with mine - it seems to really not like USB3 (Type A) ports.  I moved it to a USB2 and it's fine.

[John Vere]

Possibly related. I have 4 interfaces but I mostly use my Motu M4 because I really like the monitoring setup. 
This issue doesn’t happen with my other interfaces. 

If I have been using other apps or the internet there will be an issue with recording audio. 
 

On playback it is a subtle warble or distortion sort of like you are describing. 
My workaround is simply restarting the computer before I settle down to only using my Daw and recording. 
So try that. Totally rebooting first and only open Sonar. 
 

[norfolkmastering]

After checking the drivers and firmware were up to date, I did a factory reset of the unit and changed to one of the 'core' USB sockets which wasn't part of a plug-in USB card, in the PC.

So far it's working fine again.