Question for you looper pedal owners - tempo changing

[Blueser100]

I got the Boss RC-3 pedal and so far I think it's good. But I noticed today when I went to adjust the tempo on a stored loop it pretty much sounded like crap - underwater, oscillating sound. What is worse, there's no real metronome so I have no idea how fast/slow I'm playing. (I'm practicing fiddle tunes so BPM is important to me).

My question is: Do all loopers sound like this when you change tempo of a stored loop or is it just this model? Maybe the Jamman Solo or Boomerang is not like this?

This may be a make or break issue for me. Thanks.