I just upgraded to 18.04, and I noticed that the sound from my headphones, whether plugged into front or back port, was very crackling and slow/delayed. This issue didn't exist on 17.04/10. It also doesn't affect audio coming from HDMI via Radeon 560 GPU, just the headphone/onboard audio. The relevant device is:
00:1f.3 Audio device: Intel Corporation Sunrise Point-H HD Audio (rev 31)
I have found something that at least makes it listenable - changing "default-fragment-size-msec" from 25 to 5 in /etc/pulse/daemon.conf. It makes it much much better, but still a little crackly from time to time.
I've googled for 30 min or more now, and not finding anything else that seems recent and relevant, so wondering if I should maybe open a bug, or if there's something I'm overlooking here.