I don't associate a plastic sound with Mine, but that could just be me. My personal has one of the shafts with a quick/hard, and It is pressed on top of that. sounds more like a solid board hitting the cue ball on end to me. It's a solid sound.
If it is making a flapping, papping, clicking, or ticking sound, then maybe a air gap, part of the tip coming unglued, or a lamination coming loose in the tip. You have to be carefull pressing mooris or they can delaminate. I had it happen once, I then starting backing off the pressure I used while pressing them, and have since to have It happen again with those tips, but it did happen when I overpressed that one time, so It's possible.
A loose ferrule can possibly make a simular noise also. I had one fool me into thinking it was the tip, and turned out to be the ferrule, I just could'nt twist the ferrule any, so assumed it was tight. Had loose inserts make simular sounds too, but It was easier to tell that It was farther up on the cue then at the tip or ferrule.
Another possibity is the tip is slightly miscueing if it's shined over really badly.
Without hearing It in person it would be hard to tell though, because there are so many different sounds to go on, and I know atleast I could easily misunderstand descriptions of them.
If It's a solid sound, then I would'nt worry about It much unless It's effecting your game.
Could even be Possible the tip is just too hard for your style. I put on soft, medium, and hard tips, and from what I see It really has nothing to do with skill level, just individual preferences. Personally I prefer a hard tip, but know players My level or higher that use softs, so it's really subjective.
If it were me, and it was to the point that the sound got in My head, irritated Me, and I did'nt think I could get over it, I'd probably try a different tip. That's assuming that there was'nt a hardware or installation problem. The sounds I most dislike are the ones I described above, they tend to erk me because I know something Is'nt right with the cue. even if the cue does'nt effect My game, the sound will.
Greg