There was a paper published by the Astronomical Journal in April, 1965 ( vol. 70, page 193) by Paul D. Jose which described just such an effect. He noted that the Sun and planets orbit about a point called the barycenter of the solar system which is located between 0.01 and 2.2 times the radius of the Sun from the Sun's center. The path of the Sun is actually a loop-de-loop about this point which doesn't close upon itself like an ordinary planetary orbit. Jose discovered that although this motion is complicated, the Sun returns to roughly its starting position with respect to this point every 179 years, which he noted is 9 times the synodic period of Jupiter and Saturn. This means that every 179 years as seen from the Sun, Jupiter and Saturn return to the same spot in the sky. He looked at the sunspot record from 1610 to 1954 and found evidence of this same period in the maxima and minima of the 11 year sunspot cycle. In other words, superimposed upon the 11-year cycle, there was a 179 year modulation of the amplitudes of each cycle. This modulation matched the phase of the rate of change in time of the Sun's angular momentum (dL/dt) with respect to the barycenter. He concluded that "Certain forces exerted upon the Sun by the planets are the cause of the sunspot cycle"
A quick citation search of the literature shows that even by 1990, this paper is still getting about 2-3 cites per year by other researchers who study long-term changes in the Sun's sunspot cycles, luminosity, and other factors. In 1974, an article appeared in Nature ( vol. 250, page 398) by Theodore Cohen and Paul Lintz which argued that Jose's 179 year periodicity is not externally-produced, but is a simple beat frequency. They constructed a time spectrum of the sunspot data and discovered that there were significant peaks at periods of 8.3, 9.8, 11.0 and 95.8 years, and that the 11 year and 9.8 year periods which dominate the sunspot 'cycle' had a beat frequency of 181 years, very similar to Jose's 179 year modulation period.
In 1990, astronomers James Shirley, Kenneth Serber and Rhodes Fairbridge studied the frequency content of the solar irradiance measurements returned from the Nimbus 7 satellite over an 89-month timescale ( 7 years) and noted that the variations in the total solar brightness did change with the 'second derivative' of the solar angular momentum ( d^2L/dt^2), and are primarily caused by Mercury and Venus. They also predicted that there ought to be modulations caused by the Earth and the outer planets, but 89- months of data is too short to detect these much longer-term oscillations of the solar irradiance.
These authors refer to Jose's work on dL/dt correlations, only in a brief comment in a figure caption. Most of the references are directed towards papers by Fairbridge and Shirley , and by Wolff and Hickey in 1987. These appeared in the journals Solar Physics ( vol. 110 page 191) and Science (vol. 235 page 1631). The Fairbridge and Shirley article is very generous in referring to Jose's 1965 article, and provides an extended discussion of the significance of his discovery in the context of other studies of long-term solar oscillations. They note that the interaction between the planets and the Sun which modulates the sunspot maxima cannot be tidal because the tidal forces of the planets at the solar surface is one TRILLIONTH of the gravitational force at the Sun's surface. They speculate that there must be some direct, inertial coupling between the Sun's motion about the barycenter and its internal convection pattern which generates the 11-year cycle.
At the present time, this is somewhat of a mystery. It doesn't point to any non-gravitational forces, but to some very interesting gravitational or inertial interactions between the sunspot cycle and the Sun's position ( actually the first and second time derivatives of its angular momentum) with respect to the barycenter which can be located anywhere from inside the Sun, to 2 times the Sun's radius from its center.