Almost certain it is the cabin alt warning. Make sure you have setup the air con panel on the overhead panel correctly before takeoff ie.
Cruise altitude set
Toggle switch to FLT mode
Everything else to Auto
Slightly to the left is the big dial and the small dial. Check them during your climb, big dial shows the differential pressure, keep it within limits, small dial shows the rate the cabin is pressurizing, should show a positive value to show it's pressurizing.
If you get the beeping, sounds like the cabin isn't pressurizing, so the big dial will be in the alarm zone, there is a Alt Horn Cutout button where you can silence the alarm.
See pic below (not from IXEG, but is same or very similar).