Larryi's comments are correct. If your amp is true Class A all the way, it will be hottest at idle. I think your amp is in fact AB.
I have specialized in thermal design for some time now. A two degree difference is insignificant and may not even be related to the bias. For instance, do both heat sinks have the same support under them? If the airflow through the right side heat sinks is even slightly more impeded than the left, you will get a difference. It takes very little for such a small change.
Also, thermal resistances between the devices and the heat sink is mitigated by a thermal pad. The actual thermal resistance is determined by how tightly the devices are screwed down. It could be that the right side ones are slightly tighter than the left side (common in manufacturing) - but the bias may be the same for both.
What type of temperature probe are you using? Is it a thermocouple? If so, you HAVE to use thermal paste on the end of it. Otherwise its error can be +-3 degrees.... But then thermal paste will make a mess on your heatsinks very easily. If you are using a infra-red gun, their error is even greater and it isn't simply a bias error you can back out with relative measurements - it will depend on th reflection and emissivity of the spot you are shooting.
Arthur
I have specialized in thermal design for some time now. A two degree difference is insignificant and may not even be related to the bias. For instance, do both heat sinks have the same support under them? If the airflow through the right side heat sinks is even slightly more impeded than the left, you will get a difference. It takes very little for such a small change.
Also, thermal resistances between the devices and the heat sink is mitigated by a thermal pad. The actual thermal resistance is determined by how tightly the devices are screwed down. It could be that the right side ones are slightly tighter than the left side (common in manufacturing) - but the bias may be the same for both.
What type of temperature probe are you using? Is it a thermocouple? If so, you HAVE to use thermal paste on the end of it. Otherwise its error can be +-3 degrees.... But then thermal paste will make a mess on your heatsinks very easily. If you are using a infra-red gun, their error is even greater and it isn't simply a bias error you can back out with relative measurements - it will depend on th reflection and emissivity of the spot you are shooting.
Arthur