It's been awhile since we first noticed strange sounds coming from our long-term Subaru BRZ, but we finally had the issue addressed at our local dealership with the installation of a new high-pressure fuel pump, which is under warranty. We knew we needed to get the repair completed, but it hadn't been a big priority since the car seemed to be running fine. We were wrong about that.
We dropped the car at the dealer the night before the appointment and also asked them to check a few additional issues that had cropped up in the intervening months. Our BRZ had started erratically idling with or without the air conditioning running, and it had developed a new noise: a clicking sound every time we pressed the clutch pedal.
The car was ready the following afternoon, and the new fuel pump has eliminated the squeaky whirring sound that had been our constant companion; we're left with the familiar clatter of the direct fuel-injection system. As for our other issues, the service personnel wasn’t able to find anything wrong with the engine idle and they said the clutch switch noise is common for BRZs. They greased it anyway, but it didn't seem any quieter.
What does seem better is the car's performance; the engine feels smoother and more responsive. The defective fuel pump appears to have hampered the car's performance more than we realized.