Hi,
I'm getting a shitty noise out of every lowpass filter I apply. Only comes from the filter in the FX rack. The noise starts at 10k and goes to like 12.5-13K and it looks shelved. I've bypassed everything trying to find the cause but only the filter being turned off seems to stop the sound. The Multi Band seems to exaggerate it quite a lot. I noticed I'm not on the newest beta, will try updating. Searched the forum couldn't find this anywhere . 
if the first link don't work, here is a picture of the sound in pro q 2. http://postimg.org/image/cbib57gal/
Certainly update to the latest beta in "your account". If the problem persists I'd be curious if you can create it on a new preset. BTW this is the Serum forum, you'd have better search results in the Serum forum, but it's not something that's come up before.
-Steve
Hi Steve, Thanks for responding so quick. I've updated to the latest beta and it's still there. That spectrum analyzer is the first insert effect too so it's not like the problem frequency is being generated by another plug-in. I will try and duplicate the issue. I've tried everything, changing wave tables, turning off each part of serum one by one. I'm beginning to think it might be getting generated by the multiband.
It's probably not in the multiband, per se, but the multiband boosts *each* band +36 dB if quiet, so it makes the inaudible become quite audible. It's intended for very aggressive situations. Perhaps you can just post-LPF in this scenario or not use the mulitband.
Again, I'd be curious if you can re-create it in a blank patch. My guess is simply related to your automation of the filter (as I see in the picture), as there is low-level stepping noise when automating effect parameters, which is inaudible in most circumstances, but LPF->Multiband upwards comp is the sort of edge case where the inaudible can become audible.
Hi Steve,
I've tried everything, here is the preset I made
https://www.dropbox.com/s/3mgc65nemagjeyt/TEST%20PATCH.fxp?dl=0
Maybe you can have a look, the sound only happens when both multiband and LP filter enabled.
There's effectively never any highs in the patch because of the FX filter LPF( raise its cutoff and you'll hear the real highs) so the multiband is pushing extreme upward gain in the highs. It's how the multiband is, extreme. You can use an external multiband plugin if you want something less extreme. So, you're hearing what little is there which apparently you don't want, so the easy solution is to simply have no highs up there.
So for that, one option would be to simply LPF (again) after everything which you can do with the EQ. You could also notch it out by enabling the EQ around 11K notch and -24 dB.
