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Been a while since I asked for help here in this Forum. Always had good luck, so here goes. I'm having an issue that started about a month ago with a thumping sound in the right rear portion of our 2008 Monaco Camelot 42 footer. It only seems to happen at colder temps. In tracking down the source of the noise I discovered that it's the Big Boy relay in the rear run electrical bay. I've been checking forums, including this one, and really couldn't find any guidance of what the issue might be that causes the thumping sound, or what can be done to correct it. Some say to replace the relay, some say to remove the relay and clean the contacts, and some say to just live with it. But if it hasn't thumped for the last seven years, and it's just now making the sound, why should I ignore it and "live with it" now? That doesn't seem right. To give a bit of background, this only happens when hooked to shore power (nothing when dry camping and the batteries are isolated), with both the inverter and the charger side of the inverter turned ON, and only when it's pretty cool outside. During the day with warm temps ... nothing ... it's quiet. When I switch the charger side of the inverter OFF, the thumping sound stops. Now, I replaced the house batteries about a year ago with 300 amp AGM's X4 because the original batteries were shot, and haven't replaced the chassis batteries at all. They seem to be performing just fine. They're group 31P with two maintenance free Diehard's in parallel. Total CCA's to crank the engine is 1500. Now they're also about seven and a half years old. Is it possible that the Big Boy relay is trying to charge them and they're not accepting a full charge because of age, so the relay is cycling continuing to try and charge them? Last tidbit of info is this ... the control board just behind the Big Boy relay has three green LED's on it and all three are lit. So what do you guys think? Does anyone out there have any guidance that can help? I'd appreciate any help that any of you can provide. Thanks, Rick