I’ve experienced a similar issue with my electronic drum kit before, so I totally get how frustrating this can be. With your Alesis Nitro, there are a few things you could check that might help resolve the problem without needing to dive straight into repairs.
First, have you checked the master volume setting on the drum module itself? It might seem basic, but sometimes settings can get changed inadvertently. Make sure it’s turned up to an appropriate level.
Another factor could be the kit's internal settings. The Alesis Nitro allows you to adjust the sensitivity and velocity curves of each pad individually. If these settings have been adjusted, it could affect the output volume. Dive into the module's user manual (which is often available online as a PDF if you've misplaced yours) to double-check these settings.
It might also be worth testing the kit with another set of headphones or another amplifier, if possible, just to rule out issues with those. Sometimes problems that seem related to the drum kit can be traced back to peripherals.
On the technical side, the issue could possibly involve the cables and connections within the module itself. If you’re comfortable doing so, carefully open the module and check for any loose wires or connectors. But if you’re not experienced in dealing with electronics, it might be best to avoid this step to prevent further issues.
If none of these steps work, there could be a hardware fault, possibly with the module's output jacks or the internal circuitry. In that case, reaching out to Alesis support or seeking a professional repair might indeed be necessary.
For further reading on electronic drum kit maintenance and troubleshooting, you might find articles on Drummerworld or eDrumcenter useful. They often have discussions and tips specific to electronic kits.
Before making any drastic decisions, I'd encourage you to look into these troubleshooting steps. Feel free to ask if you’d like more detailed guidance on any of these points!