This sounds to me like a whistle that would happen if you’re closing your mouth and moving your tongue forward during the /ɔ̃/, just before the second /k/ sound. It would be your mouth getting into position to make the /y/ sound, but a little too early.

You can verify this theory by doing a pronunciation drill where you repeat the initial syllable /kɔ̃/ many times before saying the rest of the word, e.g. /kɔ̃kɔ̃kɔ̃kɔ̃klyr/ … sounds a bit impolite so do it where nobody who understands French can hear you

If this theory is correct then you should only hear the whistle in the last one of these /ɔ̃/ sounds (or not at all, if the drill fixes it).

EDIT: after you confirmed that this only happens at the last vowel. I’m sorry I don’t have any experience with this kind of speech issue to provide tried-and-true remedies. Just a couple things to keep in mind (here I assume, based on your usage of English in the question, that you are a student of French as a second language or “FLE”)

• First off it doesn’t impede understanding; many people probably won’t even notice it. No need to stress out too much about it if your primary goal is to be understood.

• The good news is that you’re doing the hardest part correctly: your nasalized consonant /ɔ̃/ is perfect in isolation and so is the /y/. Since many languages don’t have either of these vowels you’ve likely had to learn one or both of them and you’re doing fine.

I might still suggest a couple of things:

• Considering that you can say the syllables independently but have trouble when they quickly follow each other, maybe do a drill where you say /kɔ̃/, pause, /ky/, pause, /kɔ̃/, etc. and gradually speed up and shorten the pauses between syllables

• Do an exercise where you first pronounce the word without the initial /kɔ̃/, then with the /kɔ̃/ but a slight pause between the two parts: “currence, con-currence”, “clure, con-clure”

Hope this helps!