[Discuss-gnuradio] Audio transmitting question

Hello, everyone.

I am trying to implement audio transmitting using PSK-Modulation on 433 MHz Frequency with 1.25Mps.
On Receiver side sound appears, but very abruptly. Looks like sampling/re-sampling mistake.
Even the adding of codecs (CODEC2, ulaw..) did not helped, but added more noise. What can cause this problem, which block is responsible for this?
Thanks in advance.
Timur