Ping-Pong Playback

I'm attempting to loop an audio file of a cello drone ad infinitum, and have been trying different methods with little success. I originally tried taking the file, chopping it in half, reversing the second half, and stitching them together but I had all kinds of issues with clicks and things. I think due to the nature of the original sample, this method won't work. Interpolation errors are not allowing the ends to play smoothly. Would be happy to provide the samples if someone wants to take a look. Perhaps I'm doing something wrong though.

So I thought I'd give a Max-style method a shot.

I'm attempting to just play the file forwards and backwards...been trying with groove~ (way too clicky, I think due to not being sample-accurate with the trigger) and wave~ (as seen here). However, at the 'turnaround' points, there's a bump . I can't determine if this is my lack of knowledge in working with audio, or if I need to finesse the [pong~] in a different way. It's easy to hear with vibes-a1.aif.