High-frequency (1 GHz to 8 GHz) magnetic noise has been measured in giant magnetoresistive (GMR) devices with dimensions down to 100 nm. Both commercial recording heads and GMR devices fabricated within microwave circuit structures were measured. The uniform ferromagnetic resonance mode has been measured as a function of applied field, bias current, and temperature. In addition to the uniform mode, other modes have been observed that are due to micromagnetic structure in the devices. The presence of these modes can be correlated with Barkhausen noise in the magnetoresistance data. The data have been fit with simple models based on the fluctuation-dissipation theorem and with numerical models that incorporate more complex dissipation processes.