I've just started using the Pro Demo & I can't get rid of interference that sounds like a bad connection during use.
I get this even when recording one track, then playing it back; yet the same mic, interface and headphones work perfectly if I record through Audacity, which I want to upgrade from.
Any ideas on how to correct this would be welcome.
Thanks

Have you tried adjusting your latency settings and/or buffer size? And is the CPU meter pegged during recording or playback?

Atari 5200, 64K RAM S1PRO Radio Shack Cassette Recorder w/internal Mic,

Its definitely a setting problem but to help you we need to know a little more information, PLease give some computer specs and exactly what interface you are using. Studio One has built in low latency with drop-out protection but not sure the demo has all those features, never the less lets see what you are running as I am sure we can solve the problem.

I'm running into the same situation. I have Studio One 3 Free, latest version. I'm getting pops and crackles as well. I'm running a Win7 Ultimate machine, quad core, 64-bit, with 8 gigs of DDR3 RAM. My interface is an M-Audio Delta 66 24/96 card and I'm running its ASIO drivers. I have buffers set to 1024.
My copy of SO3 has the low latency with drop out protection feature. I've also been monitoring that screen that shows CPU activity for each track. Whenever a crackle occrs, the cpu activity for the track where it's happening jumps up to 30 or 40%. When I set the drop out protection to maximum, it also maxes out the CPU, which I don't think is good.
This machine is my DAW and it's well behaved in Sonar and Band in a Box. I've played around with other tunes woth SO3 on this machine and wasn't running into this problem. Perhaps it's something peculiar about the song I'm working with, but I don't know why. Six instruments, all MIDI, each assigned to its own track.

Best,
Michael

Try setting Dropout Protection to low. I was getting bad CPU spikes with just a few plugins and FX operating. I tinkered with a few things, and when I set dropout protection to low, my CPU usage dropped to about 5%-10%, and no spikes.

Atari 5200, 64K RAM S1PRO Radio Shack Cassette Recorder w/internal Mic,

I have get after i switch 64 bit sound output on(On professional demo) and i notice that no sound output come on a soundblaster z with windows audio. I switch then back to 32 bit and after that i get very high cpu load and random crackles.for example the room reverb need 15% CPU load. the strange was this happen after i switch back to 32bit sound and reboot. I look in power plan setting and there was High performance setting set. normally i use balanced and have no problems with crackle and low latency in win 10.
I use windows audio because i use equalizer APO for system wide speaker calibration correction. this work only in windows audio setting and it is possible that sound device can share and the volume knobs on the computer keyboards work too. I set power plan back to balanced and s1 work since some days without crackle and room reverb need only 7% CPU load. I also test to set it back to high performance . work ok too with same cpu load. I fear when switch to 64 bit sound they change something in power plan setting, so i better never try 64 bit again.

win 10 64 I5 8600K(6*4.1 GHZ) studio one V 4 pro studio live ar8

I just solved this by getting a new Rodes condenser mic. Previously I had the Presonus condenser mic. I tried all the latency settings, replaced all my cords and interface before I figured this one out! Good luck!