John,
Sorry I can't help with your gurgling sound but I may with the audible alarm.
Volvo started installing the alarm circuit on their engines as a standard item sometime during the mid to late 1999 Volvo model year. Prior to that time, the engine wiring harness was prewired for the alarm circuit as it was an option. (Standard for EF model year, accessory for LK, BY and WT model years.)
The alarm circuit consists of a low oil pressure switch and a high water temp switch.
The temp switch for the alarm circuit is mounted in the top of the water circulation pump on the front of the engine. If there is a 3/4" plug in the top of the water circulation pump, then the temp switch is not installed. Look for a single tan colored wire with a black boot, that is what connects to the temp switch. The oil pressure switch is "T"ed off the oil pressure sender, which is located on the aft, slightly port, topside of the engine. (near the distributor, if your engine has one). The electrical connection to the low oil pressure switch is a single tan wire.
These 2 switches for the alarm circuit are electrically connected in parallel. The oil pressure switch will ohm out as a short/zero ohms, with no oil pressure. The temp switch will ohm out as an open/infinity ohms, with normal water temperature. If my memory serves me correct, the oil pressure switch should "open" at about 6 PSI of oil pressure and the water temp switch should "close" around 185 degrees.
The single electrical connection for the engine alarm circuit to the boats wiring harness is through the engine harness connector on the starboard side of the engine.
On my 1998 202BR, Crownline was kind enough to have prewired the boat's wiring harness for the engine alarm circuit. To install the alarm, it was simply install the 2 switches on the engine, find the end of the alarm circuit wire at the helm, and buy a 12 volt piezo buzzer at Radio Shack. One wire of the piezo buzzer connects to the alarm circuit wire at the helm and the other wire connects to 12 volts.
Call Volvo at 757 436-2800 and ask for tech support. Have your engine model and serial number available. Give them the numbers and they can give you the part number of the audible alarm kit. (and part number for the service manuals for your engine/outdrive) My records from 2001 indicate the audible alarm kit should be part number 3857455-4 or 3857956-1 depending on your engine model. In 2000, the kit cost was around $50 (manuals were around $80). While you are talking to Volvo tech support, I'd mention the gurgling sound. Maybe they will volunteer to disclose a little helpful information. I'd suspect you will be pulling the outdrive to inspect for a collapsed hose and replace it.
Phil Belcher
2003 266CCR
496 MAG, Bravo 3