Reaper is slowing down while recording and also making noises

[DolphinRiot]

I´m having problems with Reaper.

The thing is that If I try ti record anything using a guitar vst, it sounds slower than the tempo of the click or of the virtual drum kit, also it sonds crispy, it has a lot of crispy sound on first plan. I can't use it that way.

I also use Amplitube 4 and Kontakt drum machine by native instruments, but I-ve discard that the problem is on the plug in.

My mac version is OS Mojave 10.14.6. iMac (21.5-inch, Late 2013). 3.1 GHz Intel Core i7. 16 GB 1600 MHz DDR3.

My interface is a Focusrite Scarlett 2i2 2nd Gen.

Hope to get and answer soon

Thanks