I have this issue since I purchased the RTL510,
did many experiments and can now narrow the problem down to the distance between the edge and the RTL510,
in my case it works better if the distance is around 600mm, 640mm reduces the volume, with 740mm (flyout mount) no more sound
I reported it to Garmin and suggest everyone else with this problem should do the the same (see Garmin response below), Garmin can not fix it without good user feedback
-------------------------------------Garmin Response------------------------------------------
The Threat alert tone is different than the other alert tones and could be harder to hear for some people. I do think the difference in the type and location of the mount will make some difference here.
We will be looking into escalating this to see if the tones could be configured and turned up or down. Additionally, we encourage you to suggest to other forum participants to contact support to report their feedback on the alert tones as this will give the issue more traction.
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