I just downloaded LMMS on my mac. When I play the drum machine or play in the piano it makes clicking sounds along with the note. and when I loop drum samples it skips and is distorted. I have my buffer size all the way down. I have no idea what to do. My mac is a 2009 its not the newest but it has better audio than this I reckon.
In sound generation, loudness in excess is the main reason for distortions
Click artefact's happens when a wave-shape is initiated or terminated outside 0 dB
Those are general.

In lmms specifically using a wrong sound-device can also lead to distortion
Does this fit in your case?