Why did my PC get slower after upgrading from an RTX 3070 to an RTX 5070?

I replaced my RTX 3070 with an RTX 5070 without changing any other hardware, and my system became noticeably sluggish. Games that previously ran well are now performing terribly—for example, Deadlock dropped from around 130 FPS to about 30 FPS. Programs also take noticeably longer to launch.

My system has a Gigabyte Z490 VISION G motherboard, an Intel Core i7-10700KF, and 32 GB of DDR4 memory. I used DDU to remove the previous graphics drivers and shader cache, tried both current and older drivers, adjusted fan and overclock settings, changed NVIDIA Control Panel options, increased the display refresh rate, and reseated the card in multiple PCIe slots. None of that helped.

Could the problem be related to the power supply, PCIe configuration, BIOS settings, Resizable BAR, or a defective graphics card? Is the CPU too old for the 5070, or should I investigate the storage drive and motherboard instead? I am considering reinstalling Windows and possibly switching back to the 3070. During troubleshooting, I also noticed that one fan is making a loud grinding or squealing noise.