No, I've never had such issue with HC-05 working with Whazon.
Without seeing your project and it's implementation I can only suggest paying particular attention to how the common ground connections are hooked up together, power decoupling and filtering, as well as putting series resisters (47 or 100 ohms)on Tx and Rx connections.
I made a small class d amp that is connected to an analog audio processor, both are controlled by an atmega8. The sound comes out very well, but when including the HC-05 a noise is detected, and when sending an order from the cell phone as a remote control, the noise increases slightly.
You are right that it must be a fault in the ground points, I am checking that but it continues to a lesser extent. Do you know of any document that deals with this topic in more detail? I will be grateful.
It can be tricky, but if possible you probably could start with disconnecting the ground for the digital part of the system from the analog part of the system, including the ground of the power supplies, so that the two ground systems are completely isolated to each other, then using one single piece of wire, connect them together. Apparently, i'm assuming you have dedicated, completed isolated power supplies for analog and digital parts of the system.