Hi rw,
I can't reproduce this but here are some ideas to begin with in case it helps (let us know if you can't fix it though - may be something others do hear too of course)..
it may be your room is blooming or 'ringing' in that frequency range (different instruments have so many different overtones etc. and it may only be this instrument which kicks off the ringing), or similar with your speakers or headphones (try more ways of listening in case it's just the one speaker or headphones it seems to happen with. If it's just speakers, maybe moving them away from a wall or other things may help significantly) - it's a very common cause of this kind of thing. You can test your keyboard to be sure it's not firing a higher velocity than other keys (by clicking the Pianoteq mini keyboard - or 'Control k' to bring up a computer keyboard way to play notes).
Here are some things you can do to attenuate though (without need for Standard or Pro versions)..
in the "effects" section, select an EQU3 effect, and try playing around with these values:
Frequency: 370
Gain: -10.00
Q: 15.00
and go from there to take any extra oomph out of just that note.
I'd say, if you have the taste and desires to delve into detailing your pianos, very definitely I would recommend Pro because you can alter so much about every element of the sound (multiple small edits to many things can be extremely powerful to get entirely realistic but unique pianos of your own design - including the tiniest elements of tuning down to single notes - strike point - note by note editing of everything valuable to the whole sum of the parts), you can create whatever you plan to - including very non-piano sounds venturing into creative grounds for pads and soundscapes.
I have the Studio offering which is Pro plus all instruments - if you have the budget or have saved up, and you believe you'd be likely to eventually collect the set, it's the least expensive way to do so in the end - no regrets here - some of the best money I've spent on musical gear without a doubt - in fact, a little like a broken record at times, I do say often how pleased I am with Modartt, compared to practically all other software I've encountered over decades - practically uniquely good, not too shy to say it again.
If budget doesn't allow this, you can still target certain things like the above with EQU3 in Stage or Standard - may require some learning curve and patience which is all worth it. You can also change the EQ of the "amp" if the preset has that in the chain - may also help clear a given frequency.
There has been some discussion about guitar I was very much in the camp of "Please stick to pianos" - until lately, I'm still a leaning that way - but as development pace picks up and the tech is solidified, I can certainly see a time when more instrument types become not only doable without limiting work on pianos but maybe even (gasp) inevitable
Pianoteq Studio Bundle (Pro plus all instruments) - Kawai MP11 digital piano - Yamaha HS8 monitors