This is something that happens in simulcast systems. Your scanner is receiving multiple sites and is having trouble decoding the colliding signals. There are many other posts on simulcast distortion discussing this in greater detail.
Some things to try:
1. Have you upgraded to the most recent firmware edition? I noticed quite a bit of improvement on my local simulcast system after doing the firmware upgrade on my 396XT.
2. Set the attenuator for the Carver Scott site to ON. This dampens the incoming signal.
3. Try a different combination of settings for the P25 Adjust Level and P25 Adjust Mode. This may be painstaking as there are many combinations before you hit the "sweet sport"
4. Some folks have reported improvement using Yagi (a kind of directional antenna) pointed toward the closest tower.
5. Other folks have reported improvement using a paperclip for an antenna. The Paper Clip Antenna
6. They say having a loose/open squelch setting may be helpful.
Fortunately from what I could tell on the You Tube video, the distortion isn't as bad as I have seen on my local system. So doing some or all of the above might be successful.