Yes—this is most likely the camera’s buffer filling, then the shooting rate dropping to whatever pace the camera can sustain while writing to the SD card.

Why it happens:

• The D7000 can shoot a short burst quickly using its internal buffer.
• RAW files are large, and sustained 2 fps may exceed the camera’s real-world write throughput.
• Card speed ratings are best-case figures; actual in-camera performance is lower due to controller limits, filesystem overhead, and verification/latency.
• Some settings can reduce effective buffer depth. In particular, in-camera distortion correction can negatively affect burst capacity.

So the pattern you hear—fast at first, then periodic pauses—is exactly what you’d expect once the buffer fills.

What to try:

• Turn off distortion correction and other in-camera processing you don’t need.
• Try a faster SD card to see if sustained performance improves, though the camera itself may be the limiting factor.
• If possible, reduce RAW size or switch to JPEG if your workflow allows.

In short: the initial burst uses the buffer; the slowdown reflects the D7000’s sustained RAW write limit, not necessarily a faulty card.